realloc.3p (5600B)
- '\" et
- .TH REALLOC "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .SH NAME
- realloc
- \(em memory reallocator
- .SH SYNOPSIS
- .LP
- .nf
- #include <stdlib.h>
- .P
- void *realloc(void *\fIptr\fP, size_t \fIsize\fP);
- .fi
- .SH DESCRIPTION
- The functionality described on this reference page is aligned with the
- ISO\ C standard. Any conflict between the requirements described here and the
- ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
- .P
- The
- \fIrealloc\fR()
- function shall deallocate the old object pointed to by
- .IR ptr
- and return a pointer to a new object that has the size specified by
- .IR size .
- The contents of the new object shall be the same as that of the old
- object prior to deallocation, up to the lesser of the new and old
- sizes. Any bytes in the new object beyond the size of the old object
- have indeterminate values. If the size of the space requested is zero,
- the behavior shall be implementation-defined: either a null pointer is
- returned, or the behavior shall be as if the size were some non-zero
- value, except that the behavior is undefined if the returned pointer
- is used to access an object. If the space cannot be allocated,
- the object shall remain unchanged.
- .P
- If
- .IR ptr
- is a null pointer,
- \fIrealloc\fR()
- shall be equivalent to
- \fImalloc\fR()
- for the specified size.
- .P
- If
- .IR ptr
- does not match a pointer returned earlier by
- \fIcalloc\fR(),
- \fImalloc\fR(),
- or
- \fIrealloc\fR()
- or if the space has previously been deallocated by a call to
- \fIfree\fR()
- or
- \fIrealloc\fR(),
- the behavior is undefined.
- .P
- The order and contiguity of storage allocated by successive calls to
- \fIrealloc\fR()
- is unspecified. The pointer returned if the allocation succeeds shall
- be suitably aligned so that it may be assigned to a pointer to any type
- of object and then used to access such an object in the space allocated
- (until the space is explicitly freed or reallocated). Each such
- allocation shall yield a pointer to an object disjoint from any other
- object. The pointer returned shall point to the start (lowest byte
- address) of the allocated space. If the space cannot be allocated, a
- null pointer shall be returned.
- .SH "RETURN VALUE"
- Upon successful completion,
- \fIrealloc\fR()
- shall return a pointer to the (possibly moved) allocated space. If
- .IR size
- is 0, either:
- .IP " *" 4
- A null pointer shall be returned
- and, if
- .IR ptr
- is not a null pointer,
- .IR errno
- shall be set to an implementation-defined value.
- .IP " *" 4
- A pointer to the allocated space shall be returned, and the
- memory object pointed to by
- .IR ptr
- shall be freed. The application shall ensure that the pointer is not
- used to access an object.
- .P
- If there is not enough available memory,
- \fIrealloc\fR()
- shall return a null pointer
- and set
- .IR errno
- to
- .BR [ENOMEM] .
- If
- \fIrealloc\fR()
- returns a null pointer
- and
- .IR errno
- has been set to
- .BR [ENOMEM] ,
- the memory referenced by
- .IR ptr
- shall not be changed.
- .SH ERRORS
- The
- \fIrealloc\fR()
- function shall fail if:
- .TP
- .BR ENOMEM
- Insufficient memory is available.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- The description of
- \fIrealloc\fR()
- has been modified from previous versions of this standard to align
- with the ISO/IEC\ 9899:\|1999 standard. Previous versions explicitly permitted a call to
- .IR realloc \c
- (\fIp\fI, 0) to free the space pointed to by
- .IR p
- and return a null pointer. While this behavior could be interpreted as
- permitted by this version of the standard, the C language committee have
- indicated that this interpretation is incorrect. Applications should
- assume that if
- \fIrealloc\fR()
- returns a null pointer, the space pointed to by
- .IR p
- has not been freed. Since this could lead to double-frees, implementations
- should also set
- .IR errno
- if a null pointer actually indicates a failure, and applications should
- only free the space if
- .IR errno
- was changed.
- .SH RATIONALE
- None.
- .SH "FUTURE DIRECTIONS"
- This standard defers to the ISO\ C standard. While that standard currently has
- language that might permit
- .IR realloc \c
- (\fIp\fI, 0), where
- .IR p
- is not a null pointer, to free
- .IR p
- while still returning a null pointer, the committee responsible for that
- standard is considering clarifying the language to explicitly prohibit
- that alternative.
- .SH "SEE ALSO"
- .IR "\fIcalloc\fR\^(\|)",
- .IR "\fIfree\fR\^(\|)",
- .IR "\fImalloc\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<stdlib.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 by the Institute of
- Electrical and Electronics Engineers, Inc and The Open Group.
- In the event of any discrepancy between this version and the original IEEE and
- The Open Group Standard, the original IEEE and The Open Group Standard
- is the referee document. The original Standard can be obtained online at
- http://www.opengroup.org/unix/online.html .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .